The present invention relates to an improved connecting arm for use in a Bourdon gauge which is secured between one end of a Bourdon tube and an indicating needle driving mechanism of the Bourdon gauge by welding. The connecting arm is provided with a clamping end which can be firmly engaged with a Bourdon tube and the other end engaged with the driving mechanism first manually so that Bourdon gauges so assembled then can be automatically processed by an automatic welding machine in a consecutive order without further manual interference, increasing the speed and safety of welding assembly in practical production of Bourdon gauges.
Bourdon tubes are a well known device having widely used in all kinds of Bourdon gauges for decades that are mainly mounted onto various vehicles, ships and airplanes for mechanically measuring and indicating oil or air pressures and temperatures of such transportation means. A Bourdon tube is coupled to an indicating needle driving mechanism of a Bourdon gauge at one end by way of a connecting arm fixed in place by welding. A Bourdon tube made of copper is hollow, semi-circular and flat in structure and is tightly sealed at one end and is in communication with a pressure source or a thermal source at the other end. The sealed end of the Bourdon tube is engaged with an indicating needle driving mechanism by a connecting arm which is commonly secured in place to the end of the Bourdon tube by welding so that variations in air or oil pressure and temperature in a Bourdon tube causing the Bourdon tube to be extended or withdrawn renders the indicating needle to point accordingly to a corresponding numeral on a gauge panel whereby a driver can have instant knowledge of the operating conditions of important parts of a vehicle, ship or an airplane.
Referring to FIGS. 1, 2, a first common Bourdon gauge is mainly made up of a tube mount 10, an indicating needle driving mechanism 20, a Bourdon tube 30 and a connecting arm 40. The needle driving mechanism 20 is secured to the tube mount 10 by screws and the Bourdon tube 30 is sealedly in communication with tube mount 10 at one end. The other end of the tube 30 is coupled to the connecting arm 40 by welding which is connected to the indicating needle driving mechanism 20 at the other end. The first conventional connecting arm 40 has a digit 7-shaped fixing end 43 and a horizontal extension 41 at one end. A through hole 42 is disposed on the horizontal extension 41 in correspondence to a rivet hole 24 on the indicating needle driving mechanism 20 so that the horizontal extension 41 of the connecting arm 40 can be riveted to the driving mechanism 20 first and then the fixing end 43 is manually secured to the Bourdon tube by welding in assembly.
Referring to FIGS. 3, 4, a second prior art Bourdon gauge is similarly comprised of a tube mount 10, an indicating needle driving mechanism 20, a semi-circular Bourdon tube 30 made of copper and a U-shaped connecting arm 40 made of a copper wire. The U-shaped wire connecting arm 40 having two separated ends to form an opening 44 is led through a through hole 24 on the needle driving mechanism 20. Then the opening 44 of the connecting arm 40 is welded in abutment against the end of the Bourdon tube 30.
The designs of connecting arms used in the prior art Bourdon gauges cited preceding have the following disadvantages in production process and practical use:
1. The first and second prior art connecting arms can only be placed in abutment against the end of a flat Bourdon tube without retaining support in an assembling process, so manual labor is indispensable to hold and put the parts assembled by welding, resulting in the low speed of production.
2. The manual welding process often results in poor quality in production and air leak problems as a result of uneven welding density and poor connection at joints, making the quality of production hard to control.
3. High temperatures in welding makes the manual production process dangerous and harmful to personnel in work as a result of negligence in operation.